The present invention relates to novel oxazolidine amide (5 member ring) and tetrahydrooxazine amide (6 member ring) surfactants and to methods for preparing the surfactants. These surfactants are biodegradable, sugar-based surfactants.
It has in recent years become a highly desirable goal in the art to find surfactants which are environmentally friendly and preferably not tremendously expensive. Carbohydrate based surfactants are good candidates in this regard because they offer the possibility of cheap, renewable and biodegradable surfactants.
Several carbohydrate based amide surfactants are known in the art.
In U.S. Pat. No. 5,389,279 to Au et al., for example, there are taught certain aldobionamide compounds. These compounds are structurally different than the compounds of the subject invention.
U.S. Pat. No. 5,009,814 to Kelkenberg et al. provides N-polyhydroxyalkyl fatty acid amides used as thickeners in aqueous surfactant systems and having the formula: ##STR1## wherein R.sub.1 is alkyl, R.sub.2 is hydrogen, alkyl or hydroxy alkyl and X is a polyhydroxy group.
A series of Procter and Gamble references teach various compositions which comprise polyhydroxy amides. WO-92/06172, for example, teaches built liquid detergent compositions containing polyhydroxy fatty acid amides. There are about 20 references reciting various compositions containing the same polyhydroxy amides.
The polyhydroxy fatty acid amides are generally linear structures (i.e., wherein the polyhydroxy group is derived from monosaccharides such as in the case of N-methyl glucamide). Such linear structures would be expected to have strong intermolecular interactions leading to, for example, higher Krafft points and therefore to be less soluble than cyclic surfactants such as the compounds of the invention (Krafft point is a measure of solubility; specifically, it is the temperature at which the solubility of the nonionic surfactant becomes equal to its critical micelle concentration). Even if the polyhydroxy amide is a disaccharide, the compounds still have an extended linear structure within the molecule which differs from the compounds of the invention.
Polyhydroxy fatty acid amides with a reverse amide link from the polyhydroxy fatty amides noted above (e.g., N-alkyl gluconamides of general structure HOCH.sub.2 (CHOH).sub.4 CONHR) are also known in the art, for example, in U.S. Pat. No. 2,662,073 to Mehltretter et al. As noted, these are either linear structures which would be expected to have higher Krafft points (i.e., be less soluble) than cyclic compounds; or they have extended linear structures within the molecules which would also be expected to raise the Krafft point.
Thus, it would be advantageous to find a carbohydrate based surfactant with a structure providing greater solubility. In addition, it is always desirable to find a novel, carbohydrate surfactant, whether or not it has a cyclic structure.